import 'dart:convert';
import 'dart:typed_data';
import 'dart:io';
import 'package:crypto/crypto.dart';
import 'package:waylume_server/core/utils.dart';

import '../config/supabase_config.dart';

class RollingCodesService {
  // Shared constants (these should match edge function constants)
  static const String registrationSeed = String.fromEnvironment('REGISTRATION_SEED', defaultValue: 'default_registration_seed_change_in_production');
  static const String secretSalt = String.fromEnvironment('SECRET_SALT', defaultValue: 'default_secret_salt_change_in_production');
  static const int timeWindowSeconds = 300; // 5 minutes
  
  // Server configuration file path
  static const String configFile = '/tmp/waylume_server_config.json';
  
  static String? _operationalSeed;
  static String? _serverId;
  
  /// Initialize service and load/generate configuration
  static Future<void> initialize() async {
    _serverId = fromEnivronment('SERVER_ID');
    if (_serverId == null) {
      throw Exception('SERVER_ID environment variable is required');
    }
    
    await _loadConfiguration();
  }
  
  /// Generate registration rolling code
  static String generateRegistrationCode([DateTime? timestamp]) {
    timestamp ??= DateTime.now();
    final timeWindow = timestamp.millisecondsSinceEpoch ~/ 1000 ~/ timeWindowSeconds;
    return _generateHmacSha256(registrationSeed, timeWindow.toString());
  }
  
  /// Generate operational rolling code
  static String generateOperationalCode([DateTime? timestamp]) {
    if (_operationalSeed == null) {
      throw Exception('Operational seed not set. Server needs to be registered first.');
    }
    
    timestamp ??= DateTime.now();
    final timeWindow = timestamp.millisecondsSinceEpoch ~/ 1000 ~/ timeWindowSeconds;
    return _generateHmacSha256(_operationalSeed!, timeWindow.toString() + secretSalt);
  }
  
  /// Validate rolling code (checks current and previous window)
  static bool validateOperationalCode(String receivedCode, [DateTime? timestamp]) {
    if (_operationalSeed == null) {
      return false;
    }
    
    timestamp ??= DateTime.now();
    final currentWindow = timestamp.millisecondsSinceEpoch ~/ 1000 ~/ timeWindowSeconds;
    
    // Check current window
    final currentExpected = _generateHmacSha256(_operationalSeed!, currentWindow.toString() + secretSalt);
    if (receivedCode == currentExpected) {
      return true;
    }
    
    // Check previous window (10-minute tolerance total)
    final previousExpected = _generateHmacSha256(_operationalSeed!, (currentWindow - 1).toString() + secretSalt);
    return receivedCode == previousExpected;
  }
  
  /// Set operational seed after successful registration
  static Future<void> setOperationalSeed(String seed) async {
    _operationalSeed = seed;
    await _saveConfiguration();
  }
  
  /// Get current operational seed
  static String? get operationalSeed => _operationalSeed;
  
  /// Get server ID
  static String? get serverId => _serverId;
  
  /// Check if server is registered (has operational seed)
  static bool get isRegistered => _operationalSeed != null;
  
  /// Generate HMAC-SHA256 hash
  static String _generateHmacSha256(String key, String message) {
    final keyBytes = utf8.encode(key);
    final messageBytes = utf8.encode(key + message);
    
    final hmac = Hmac(sha256, keyBytes);
    final digest = hmac.convert(messageBytes);
    
    return digest.toString();
  }
  
  /// Load configuration from persistent storage
  static Future<void> _loadConfiguration() async {
    try {
      final file = File(configFile);
      if (await file.exists()) {
        final content = await file.readAsString();
        final config = jsonDecode(content) as Map<String, dynamic>;
        
        if (config['server_id'] == _serverId) {
          _operationalSeed = config['operational_seed'];
          print('Loaded operational seed for server $_serverId');
        } else {
          print('Configuration file exists but server_id does not match. Need to re-register.');
        }
      }
    } catch (e) {
      print('Error loading configuration: $e');
    }
  }
  
  /// Save configuration to persistent storage
  static Future<void> _saveConfiguration() async {
    try {
      final config = {
        'server_id': _serverId,
        'operational_seed': _operationalSeed,
        'last_updated': DateTime.now().toIso8601String(),
      };
      
      final file = File(configFile);
      await file.writeAsString(jsonEncode(config));
      print('Configuration saved for server $_serverId');
    } catch (e) {
      print('Error saving configuration: $e');
      throw Exception('Failed to save server configuration');
    }
  }
}